It seems that simple green would work, I use it for o2 cleaning.
Another solution is get a vintage mask.
Another is get a mask with a couple of hundred dives on it.
My science theory
Another is (not recommended for the weak stomach) put in toilet, take a dump in it, scrub with toilet brush, flush, then spray scrubbing bubbles In the mask, let set for 5 minutes then flush.
To make sure not to fog on dive hold commode handle down part way and fill bowl. This insures cold water, fit mask on and dive head in bowl, if no fogging, move on to test a good seal, while still submerged reach up with left hand and flush, if it leaks, pull mask strap evenly on both sides, and repeat testing.
P.S. If the crack in the bowl worries you, don't, objects appear 25% bigger, more than likely it is just pubic hair.
P.S.P.S. for a tropical view, insert tidybol, and remember to ascend slowly when doing so, not to get hit by tidybol mans boat.
Happy Diving