Bigger question is WHY do you smell them?
Whether or not tanks stink there should be NO odors inside RV from grey or black tanks.
'P' Traps hold water.....vapor barrier
Air Admittance Valves under sinks closing properly....mechanical barrier
Vent lines unobstructed......venting above roof line/no pressure build up
Drain/vent lines/fittings intact...broken/cracked
Personally I have never worried about tanks stinking......they are waste tanks.
But I have made sure they don't allow odors inside RV my maintaining/fixing the 'barriers' that keep stink out.
Some folks use GEO method in black and grey
Some use Happy Camper deodorizer/cleaner
Some use Dish soap
I just flush/rinse.