Thanks for the info guys. I just tried it out, three different mixtures.

1. Vallejo umber shade (wash) thinned 1:1 with water.

2. Vallejo umber shade (wash) thinned 1:1 with Vallejo 70.524 thinner medium.

3. Vallejo umber shade (wash) thinned 1:1 with Vallejo glaze medium.

I applied all three in different spots to the top surfaces of a model I had glossed with Future. The wash with glaze medium seemed to work the best for me. It had the best flow, and gave me the best chance of cleaning up excess wash with a moist q-tip.