Thetford 96527 Blaster Holding Tank Cleaner Pouches, 1.6 oz., White (Pack of 4)

The first 2-in-1 tank cleaner specifically formulated for black/gray water and portable tanks
Cleans overnight – then just dump and go
Micro-foam action improves surface contact to vertical tank walls

Amazon.com Price: $9.81 (as of 27/11/2022 09:46 PST- Details)