This depends on what is in the tubs! Sorry you need to be a little more clear...

At the last count I have 40 containers of various sizes. Some rather large and some shallow with succulents.They have anything from a huge Crinum to fuschias, geraniums, and Heucherer. Lavenders, Pineapple lillies, Begonia, trailing plants......also some old shallow sinks with sempervivums, pinks. As MG says it depends...on plant size, type, placement, sun shade, semi shade. If this heatwave continues, I will get lots of exercise checking over them and watering, according to how heavy or dry or wilty or if I can pick them up without risk. I never use a hose on them, or a full size watering can. Just water them well in this heatwave ,if it is with you in Fife. After awhile you will learn by experience what is needed to keep them happy.

No heatwave here Dorjac...

Check to see if a container needs watering by doing the following;
Push a bbq skewer down amongst the plants' roots. Leave it there for a few minutes before removing it.
If its dry/nearly dry - water. If its wet - don't.

Dampen the surface of the soil with a spray before watering to reduce water flowing off the soil surface and down the inside of the container. Water gently several times until water seeps through drainage holes.