Step 1 — Uncover the Tank
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 (see Figure 1
below) and mark the scum stick where it crosses the reference point (A).
- 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 (B).
- Remove the scum stick and measure the distance between the two marks. This is the thickness of the scum layer (SC).
Figure 1 - Click diagram to enlarge
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 (C in Figure 1).
- 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 (D in Figure 1). The distance between the two marks (C and
D) 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.
NOTE: In the above picture, looking down an outlet baffle, the effluent is below the pipe, indicating a bad seal.
- The crossover baffle should also be free of obstruction.
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.