Before an event I spray my horse’s tail with mane and tail spray, vaguely brush it through to get it spread evenly through the tail and then plait it loosely securing it with a plaiting band at the bottom. I leave it in overnight until at the event.
The tail brushes through really easily, has additional volume, has stayed clean while travelling and has no straw or shavings from overnight that need to be got out.
If you need a bit more help to keep the tail clean while travelling, I use an old pair of tights. Feed one leg inside the other to form a single leg tube of double thickness. Feed the end of the plaited tail into the toe and pull the tights up, carefully feeding any straggly bits into the tube. Wrap the waistband and “bum section” round the top of the tail (which could be properly plaited or dampened) and secure in place with a bandage. Cheap and easy. You could get really trendy and choose a pair to match the colour of your horse or your rugs!!
I’m a bit agricultural. I use the disposable long orange gloves we use for calving. (Added bonus of desensitising horse to things rustling behind it!)