you might suggest he try goof off or goo gone, both are designed to
remove all sorts of nasties. available at places like home depot and
lowes

a friends 3 year old used markers to paint a newly painted room, goo
gone took all the marks off.

right after that her hubby was playing with her son and spilled a can
of contact cement on the kitchens vinyl floor....... a week later i
asked did you try goo gone? she hadnt but did and the you would never
know contact cement had spilled there....

a mild abrasive like a scothchbrite pad normally used to clean pans
may help remove the printing...

my friend now gives a container of goo gone and goof off to every new
baby shower mom. she reports most have thanked her.

that plastic tubing is cheap and may be available without the
printing.....

at least he could do large quanties outdoors on nice days.

so once a month do a big bunch and use as needed