Septic Tank Installation Guidelines


All tanks manufactured at Glacier Precast Concrete have been inspected and tested at the manufacturing plant. Proper installation of each tank is critical for it to function properly and remain water-tight. Many of the problems experienced with tank operation, or of tanks leaking (either water flowing into or out of the tank), or of premature system failure can be attributed to incorrect procedures during installation. Improper installation practices can seriously damage the tank, and can even cause serious personal injury. This installation guideline is offered to assist the installer with advance planning, proper site preparation, safe handling and sound installation procedures. It should also prove helpful to designers, inspectors, and homeowners. It is one of the essentials for long lived systems.

Site Conditions

PLAN YOUR PROJECT…. You will need to know the invert elevation (the measurement from the underside of the tank to the bottom of the tank’s inlet opening) in order to prepare the sub-bed elevation and allow the tank to properly receive the sewer pipe coming from the home or building. Review the manufacturer’s most current literature or website or call us at 406-752-7163 for these critical dimensions. We will be happy to assist you.

Keep in mind that the site where the tank is to be placed must be accessible by large and heavily loaded trucks weighing potentially up to 80,000 pounds. This site must allow for reasonable access under the trucks’ own power and without need for pushing or pulling. It must be cleared of trees and branches, large rocks, overhead wires, underground utilities and other structures that could be damaged by or interfere with the delivery and off loading of the septic tank. Typically, the delivery truck must be able to safely get to within three feet of the excavation to safely unload and set the tank. The purchaser/installer is responsible for any damage to the work site, the delivery vehicle or the tank as soon as the truck leaves the public roadway and enters the work site. Therefore, adequate access for delivery equipment to access the excavation and unload the tank is important. Standard concrete septic tanks are not designed to bear traffic loads or carry heavy equipment of any kind. Therefore, it is wise to install a special tank designed for traffic loadings or special situations. These are available upon request.


For the safety of your backhoe (excavator) operator, and the public good, all buried utilities should be identified and located BEFORE YOU DIG!!!!

Here is the recommended procedure: At least 24 hours before you intend to dig, submit a locate request for the dig site by DIALING 811. More information is available on this website:

Utilities Underground Location Center (UULC)

Call: 1-800-424-5555 (or 811)

Coverage Area:
All of Montana

UULC will contact the affected utilities who will send someone to mark their underground lines, or advise you if their underground services are unaffected by your proposed excavation. DO NOT BEGIN DIGGING UNTIL LOCATES ARE IN PLACE. Lay out the hole a minimum of 18” larger than the tank, to allow space to properly compact the backfill material. More space is recommended for worker safety: and it is recommended that no worker should enter the excavation until the tank has been set. Excavation walls should be sloped for stability and worker safety.

Proper bedding is important to ensure a long service life of an onsite septic system, and to allow the tank to be set level. A layer of pea gravel or sand of 5-6” minimum is recommended overlying a firmly compacted and uniformly level base. Correct compaction of the underlying soil and sand/gravel bed is critical to insure the tank is set level and stays that way. Tanks will be damaged if allowed to bear upon large stones, boulders, or rock edges.

Tank Placement

First step upon arrival of your new tank is to inspect the tank while it’s still on the truck; making sure you have received the correctly configured and sized tank as ordered. If there are any discrepancies, point them out to the driver and compare the tank to the Bill of Lading or Sales Order. Secondly, inspect the tank for any possible damage that may have occurred in transport.

Prior to placement the tank’s orientation should be confirmed with inlet openings facing the residence and discharge openings facing the drain field or treatment facility. After placing the tank, make certain that it is level and that the inlet elevation will match up with the pipe coming from the house at the point where they meet. Be certain the pitch of the inlet pipe coming from the house to the tank meets local codes. Setting of the tanks should be done by the manufacturer’s truck driver. This will insure that it is handled properly and with the correct equipment or special lifting apparatus as needed.

Industry Policy requires that “all employees shall be kept clear of loads about to be lifted and of suspended loads. (OSHA Rule #29 CFR 1901-184 -9)


Care should be taken when backfilling to prevent damage or misalignment to the entry and exit piping, the tank and fittings, and any other pipe joints. Backfill should be placed in uniform mechanically compacted layers of less than 12” thickness. Do not backfill and compact one or two sides before backfilling the opposite sides. Excavated material can generally be used for the backfill, but should not contain any large stones.

Concrete tanks are significantly heavier than fiberglass or HDPE tanks and are least likely to float in a flooded excavation. However, even concrete tanks can float if the water level around them rises sufficiently. To prevent this from happening, keep water pumped out of the excavation until backfilling is completed, or fill the inside of the tank with water as you backfill, keeping it roughly level with the level of backfill. This helps hold the tank down and provides some protection against damaging the tank during compaction efforts. Tanks rated for standard usage should never be covered with more than 6’ of soil. Installation of tanks that will be over this depth requires special traffic rated lids.

General Notes

WARNING Do not enter the tank! Confined spaces can contain hazardous gases. Only trained personnel with proper testing and protective equipment should consider entering a tank, and never alone.


The size of a septic system and tank are determined by the number of bedrooms in a home and the rate at which water flows through soil on the subject property. When planning a septic system, be sure to consider future needs for expansion. A septic system will not function properly if it is overloaded. There is no warranty for tanks which are under capacity or not properly sized and properly installed. Glacier Precast Concrete recommends the tank size be increased by 500 gallons (septic chamber) if the owner installs a garbage disposal (grinder) or expects to do so in the future. We also recommend that all tanks include an effluent filter. In addition, it is important that all entry and exit piping is connected with flexible compression fittings, in conformance with ASTM C 1227 and C 923.

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