Measure sludge and scum with a sludge judge to validate pumping need

https://romeo-wiki.win/index.php/The_House_owner%27s_Guide_to_Budget_Sewage-disposal_Tank_Emptying_and_Upkeep

Step sludge and scum with a sludge judge to verify pumping requirement, then mix contents gently to suspend solids so the vacuum truck gets rid of both layers, avoiding obstructions and early refilling.