My tendon boots went mouldy. They went in the washing machine and although they came out fine the mould was still there. So try we're then jet washed! Still fine and mould gone too!
When they were in the washing machine we had them in a pillow case
My NEW tendon boots wash well. My first pair of eskadron fetlock boots got eaten by the washing machine have washed the replacements in a bag ever since and it's been fine. Not sure what happened to the first set