Not being a smart ass but those words in the same sentence bring me nightmares;
Holding - tank - sealant - black.
There is a company in Southern California called Inca Plastics, perhaps it is better to put in a new black tank?
In the first few weeks of ownership before I lifted my rig 3 differebt times higher & higher, I got beached driving very slowly in a restaurant parking lot - the mickey mouse operation known as MEYERS RV (now out of business), tried sealing everything but its a truck, not a house, its always subjected to forces - I limped along for a year with that gray water smell surrounding my rig.
Changing it out, instant peace of mind.
05 Roadtrek Versatile 190/Super Modified & Lifted with Custom Battery Box, Two 225ah Lifeline 6 Volt AGMs in Series, 250 watts Solar, Victron BMV712 Meter & Victron MTTP 100V/30A Solar Controller, Magnum MMS1012 Inverter Charger, Onan Generator, Novakool R3800 Fridge & so very much more ...