That's exactly what I use;

a "Y" with shut-off valves on each end. I find it in the garden hose section of the hardware store. There is great advantage to filling buckets of RO water on top of the washing machine. When,
not if, you forget it's going, the overflow can be used to wash the next load.

I have also filled RO buckets from the pure water line I ran over to a bathtub. No worries, no upset wife.

BTW, how is the nuisance hair algae doing?
Aloha,
Mark