I swear by the "GEO" method:
One cup Calgon water softener ( or 20 Mule Team Borax)
One cup cheap laundry detergent - I use powder because it's easier to store
Mix in 3-5 gallon water (we use 3 gallon mop bucket because it's handy)dump down toilet and a batch in bathtub .
Leave in tanks till full enough to dump, rinse, repeat and leave in tanks .
We premeasure and keep in zip lock bags in bathroom.
Senders work fine-every time.
"wine is a constant proof that God loves us, and loves to see us happy" ben franklin