Splitting tenant caused plumbing repairs between two tenants in duplex

[Ian Noble]

I rent a duplex outside Austin Texas that has a sewage pump/grinder system set up to grind waste and pump it from the duplex to the city sewer lines. The sewage from unit A and B fall into a shared sewage tank. Over the last 3 months, I have had two issues with the pump impeller getting lodged with baby wipes. I spoke to both tenants and sent an email with photos identifying the cause of the cause damage, and as expected, the tenants on both sides denied the use of any such product. As a result, I informed them in an email that only toilet paper is allowed in the system that any further instances of baby wipes or like products that become lodged in the impeller and create the need for a plumbing company to fix & dislodge will be billed back to the tenants. Since this is impossible to identify which tenant it comes from (1 tank shared from both unit A & B), I informed them if it happens again they would be splitting the cost if neither party admitted use/fault.

After the email notice, it happened again 8 days later. Another $390 bill from plumbing company to pump and dislodge a baby wipe from the grinder. Since both tenants deny any use of wipes, and they have been recently notified in writing (email) it would be their equal responsibility for futher occurrences, can I legally charge them for this? I planned to remove it from their deposits I am holding.

Can I legally do this? If not, what other suggestions do you have? Since I have had this now happen 3 times since October 2023, I have accumulated $1100 in charges from the plumbing company.

Thanks for any input in advance.