The Thetford Level Gauge Cleaner will keep your electronic tank monitor reading accurately. This patented formula will eliminate level sensor problems caused by tissue, waste, sludge, and soap scum build-up. For the best result, use regularly. Safe for all waste treatment systems. 8 oz./40 gal. tank.• NOT for use in fresh water tanks• Superior probe and tank cleaner• Works in both grey and black water tanks• 100% biodegradable• 19-oz. bottle Works in grey & black water tanks 100% biodegradeable | Thetford Level Gauge Cleaner - 19 oz in Black