Clogged Drain Diagnosis Chart
Drain Repairs for Building Owners/Managers

Check for an outdoor cleanout access to see if water is standing in the pipe outside the building. If no water is found there, the blockage is inside the building.

Try a plumbing snake; if no success you need a professional plumber.

See BLOCKED DRAIN REPAIR METHODS

Often caused by roots in the drain line or a collapsed or broken or partly collapsed drain line.

Frequent power-snake operation can break old drain piping; trees too close to the building or to piping, especially with older pipe designs are often invaded by tree roots.

To determine where to try reaming the drain line, inspect the septic tank wastewater level. In a two-chamber septic tank if the outlet chamber is above the outlet pipe, the problem is probably downstream from the septic tank.

If the waste level is at the outlet, or if you have a single-chamber septic tank, measure the scum and sludge levels.

MEASURE SEPTIC TANK SCUM & SLUDGE. If these levels are above the limit, pump the septic tank immediately.

If the septic tank inlet is clear, the pipe between building and septic tank is probably blocked and needs to be cleared. You need a professional plumber.

See BLOCKED DRAIN REPAIR METHODS

See DRAIN vs SEPTIC for more help in distinguishing these blockages.

You need a professional plumber. Snaking the line may discover the location of the collapsed or broken piping.

You need a professional plumber.

See BLOCKED DRAIN REPAIR METHODS

Check for clogged piping leaving the septic tank, at the D-box, or in the drainfield.

Check for an inoperative siphon or pump.

Check the siphon vent pipe to see if wastewater is flowing into it. If not see the two causes listed just above in this table.

If water is entering the siphon vent pipe see topic C. below

See "B" above. If wastewater is flowing into the vent pipe, pump the dosing tank & inspect/repair the siphon. A broken bell can block the siphon.

If the bell is undamaged, remove the bell and snake the siphon for blockage.

If the siphon is not damaged or blocked, see the final two diagnoses in "A" above.

If a blockage is found you need a professional plumber familiar with dosing system equipment.

If wastewater flows out of the dosing tank, pump the tank & inspect pipes & siphon components for damage you need a professional plumber to do this.

Dual siphons occasionally may stop alternating as they should. The septic system may continue to appear to function but you may be overloading one portion of the drainfield. If siphons only rarely fail to alternate, it's not a significant concern .

If one of the siphons is not working at all, see "C" above.

Excavate gently, find the break, repair or replaced the damaged section.

Diagnose the cause of the breakage: driving over the piping, frost damage to a clogged line, roots, buried rocks, poor original installation. Look for tree root invasion causing a break - you may need to remove nearby trees or shrubs.

Determine the cause as in "A" above - probably the problem is downstream from the septic tank. Start by finding and inspecting the Distribution box.

If it's not flooded, the problem may be in the piping between the septic tank and the D-box.

Otherwise the fields and field piping may be damaged or flooded. This may be an indicator of a septic field at end of life, improper installation, local groundwater flooding, etc.

Failed septic drainfield, temporarily overloaded drainfield, flooding by groundwater from other sources

At mound systems remember to inspect carefully around the lower edges of the mound, especially at the lowest end of the leach bed lines.

Inspect nearby ponds, streams, culverts, ditches.

Failure to pump septic tank increases the risk of a field failure;

Inspect for external sources of water around the drainfield and re-route, install a curtain drain, or take similar measures if this is the cause.

A septic dye test can help distinguish between septic effluent failure and a drainfield flooding due to local groundwater or surface runoff problems.