Inspecting your Septic Tank
The Stick Test
Septic tanks are mainly settling chambers. They allow time for solids and scum to separate out from wastewater, so clear liquid can safely go to the drainfield. Over time, the scum and sludge layers get thicker, leaving less space and time for the wastewater to settle before passing to the drainfield.
For every gallon entering the tank, one gallon is pushed out into the drainfield. So it is important to keep the level of scum and sludge from building up and nearing the inlet or outlet baffles, where the scum or sludge could plug them up or be carried out to the drainfield.
Septic tanks should be checked for buildup every 1 to 3 years until you can get on a predictable pumping schedule. Most septic tanks need pumping every 3 to 5 years. How often depends on the size of the tank, the number of people in the household, and the amount and type of solids entering the tank.
You can hire a professional or inspect your septic tank yourself. The “stick test” procedure will guide you through the steps of measuring the amount of scum and sludge in the tank, discovering the working capacity of the tank, and determining whether the tank needs pumping. A more complete inspection includes inspecting the condition of the baffles and the pipe seals into and out of the tank.
What You Need to Do the Stick Test
- two 10-foot PVC pipes*
- four end caps*
- one 90° elbow*
- PVC cement (blue cement used in rain and wet)
- two adapters, SxMPT, threaded*
- one coupler, threaded*
- two feet of white rag or old towel or old gym sock
- string or duct tape
- pencil or waterproof marker
- rubber gloves
- disinfecting solution made of 1/4 cup bleach per gallon of water in a bucket
- plastic bag for disposal of towel, rag/sock, gloves
*all PVC materials are 1/2-inch Schedule 40 PVC plastic
The scum stick at right is 6 feet long with a 6-inch leg. The sludge stick is two 5-foot sections screwed together. (NOTE: Scum and sludge sticks can be any length up to 10 feet.)
Step 1 — Uncover the Tank
First uncover and remove the first manhole cover. Some systems have “risers” that make this job easier by bringing the tank lids up to the ground surface. (We encourage you to have risers installed so you won’t need to dig down each time you inspect.)
The diagram at left shows the top of the two most common septic tank configurations. The upper figure is found on newer tanks and the bottom one is usually found on older septic tanks. In most cases, the hole to the left is the first compartment, the hole to the right is the second compartment, and the rectangular cover is to the crossover baffle. (Some tanks, 25 years or older, may have only one compartment that is round, oval, or square.)
Step 2 — Measure the Scum Level
This procedure determines the thickness of the scum level (SC).
- To make the scum stick — Cut one of the 10-foot PVC pipes to 6 feet. Glue a 90° elbow to one end. Cut a 6-inch piece of PVC pipe and glue to elbow. Place end caps on open ends.
- Lay a board or stick across the top of the hole, manhole, or riser.
- Place the scum stick down the manhole of the first compartment of the tank until it rests on top of the scum layer and mark the scum stick where it crosses the reference point .
- Work the stick through the scum layer, leading with the elbow end. Push straight through the scum layer, turn the stick 90°, pull up on the stick until you feel the bottom of the scum layer.
- Mark the scum stick where it crosses the reference point .
- Remove the scum stick and measure the distance between the two marks. This is the thickness of the scum layer (SC).
Step 3 — Measure the Sludge Level
This procedure determines the thickness of the sludge level (SL).
- To make the sludge stick — cut the other 10-foot PVC pipe into two 5-foot sections. Glue an adapter to each stick. Screw the coupler into one of the adapters. Connect the two sections to make a 10-foot stick.
- Tightly wrap two feet of a white rag or old towel around the bottom of the stick. Fasten it with tape or string.
- Make hole in scum — do not stain the sludge stick with scum.
- Carefully lower stick through the hole in scum in first compartment until it rests on top of the liquid layer. Mark the stick where it crosses the opening of the manhole or riser
- Lower the stick to the bottom of the tank. Hold the stick in the tank for at least five minutes to allow sludge particles to adhere to the towel.
- Mark the sludge stick where it crosses the board . The distance between the two marks is the working depth of the tank (WD).
- Carefully remove the stick. There should be a distinct dark stain on the rag. Measure the height of the stain. This is the depth of the sludge layer (SL).
WHEN TO PUMP Pump the tank when the sludge depth, plus the scum depth, is greater than one-third of the working depth of the tank: (a) SC _____ inches + SL _____ inches = _____ (b) WD _____ divided by 3 = _____ If (a) is greater than (b), the tank needs pumping. For example, if SC = 10, SL = 8, and WD is 48″: 10 + 8 = 18 inches and 48/3 = 16 inches… 18 is greater than 16, so the tank needs pumping. |
Step 4 — Inspecting the Baffles
Remove the covers over the inlet, outlet, and crossover baffles. Inspect the baffles to ensure they are present and not severely corroded. If the baffles are concrete and molded into the rest of the tank, venting holes should be present and unobstructed.
- The inlet baffle should be unobstructed and the pipe sealed to the tank.
- The outlet baffle should be unobstructed and the liquid level should be at the bottom of the pipe, not below the pipe or above the bottom of the pipe. The pipe must be well sealed to the tank.
Cleanup and Disinfection
- Wear rubber gloves.
- Discard soiled gloves and sludge toweling in a plastic bag.
- Rinse sticks with bleach water to disinfect before storing
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