Aye turpitz64,
Depends what the washer you have, is made from.
Soft aluminium washers eventually deform and won't seal, so a light smear of a quality gasket 'goop' on the base threads of the drain plug and inner surface of the soft washer after cleaning, may extend its working life and ensure the plug stays put. [Torque 30ft/lbs or 30Nm]
If you have copper washers, they should be annealed (softened, all the atoms aligned the same way) before re-fitting. Heat to a cherry red all over then quench by dropping in cold water. You may still care to apply the goop and do apply the same torque when tightening. The same procedure can be applied to aluminium but you maybe left with a 'blob' of molten metal quicker than you expected!

Steel washers won't do the same job as they are too hard. I have never used fibre washers for this job, but others may have found them satisfactory.
Enjoy the wee beastie!

Regards, Bill.