ACH pulls for irregular dollar amounts

[Michael Herr]

Been using ACH pulls for rent payment through eRentPayment.com and love it, but only works if the dollar amount stays the same each payment.

Looking for suggestions on controlling ACH payments for reoccurring bills with a non-regular amounts. 

How do you automate tenant paying a sewer Bill for example?  (around $50 quarterly that can only be in owner's name)

I'd like to setup something similar to how utility bills can be deducted from the customer's account even though the dollar amount can change each bill.