I hope you're not bandaging her legs and tail in the paddock? :/
I rug my grey 24/7 with a combo or standard rug with neck rug, and a waterproof tail bag.
Basically every time he is worked, I hose/sponge him off to get rid of most of the dirt on a day to day basis.
Shampoos that have a blue or purple base are most effective at getting a grey gleaming. Start with a regular shampoo to get the bulk of dirt off, then rinse off, and lather with a blue/purple shampoo. Rub in using a body brush, washing mitt or similar. Leave to soak for a good 10 minutes then rinse off. Repeat if necessary.
As for tails - they are the first part that I wash. So soak the tail, wash with ordinary shampoo, rinse then lather with purple/blue shampoo and allow to soak until you are ready to rinse the coloured shampoo off the full body.
Follow on with a good conditioner, allow to soak, comb through and rinse out.
Once dry, I like to spray with a coat conditioner/dirt repellant and rug with freshly washed rugs and tail bag.
Greys just need a lot of good management to keep clean, if you make sure you don't allow mud and grime to settle for too long, and keep washing rugs (I was rugs every week and have a spare set while the others are drying)/tack.