From everything you've said it sounds like loaning him money will be tantamount to lighting it on fire and flushing it down the toilet.

And make sure your tenants don't have to flush repeatedly because you reduced the tank's capacity.

Ensure high rated flush ability (HD and/or Lowes actually shows how good on scale of 1 to 10 the toilet flushes.

During my initial walk through I flush the toilet and word for word say "see the toilet working properly...if it gets plugged that means you or your guests put something down it and you will be responsible plunging it and/or paying a plumber.

Think about it from a legitimately flush renter's perspective: every time I've rented an apartment, I asked if I could get a discount by paying for a few months up front.  

This is a function of flushing out a good price as a Seller.  

So when they flush and let go quickly, it may get stuck and water would keep on filling the bowl and eventually overflow.We had our contractor replace the part and the issue was supposedly fixed.

Aloha White LH (478-640) Toilet – Dual Flush by Glacier Bay (215-583) Vanity – 24?

As Mike is asking, what are you trying to flush out?  

There's a one in about 40,000 chance that one hand of video poker will result in a royal flush.