Once you’ve made your primary decisions, built the pond and done the waterfall, the plumbing of the water feature comes next: the easy part. All you need is soft black (class 3) pipe (tubing) and a few plastic “elbows” and stainless steel clamps. Remember that you will have to clean the filter of the submersible pump (See post: “What you need to build a water feature“) from time to time. This means that you’ll have to place the pump somewhere where you can easily reach it. In my case the pipe swivels around the last elbow taking the pipe over the edge of the pond to the pump. So whenever I need to clean the filter, I just “swivel” it out at the last elbow. This also means that the electric wire going to the pump has to go in there as well, otherwise the wire might prevent you from “swiveling” the pump out!
The pipe goes around the back of the waterfall and is concealed /camouflaged by rocks and plants, then straight up at the back of the waterfall and into the top layer with an elbow. The incoming water is forced downwards into the top layer by another elbow to prevent spilling. It is concealed by a piece of slate, which has been removed for this picture.
Float valve: How do you intend topping up the pond? You can make it very easy for yourself by linking in to the high pressure plumbing network at your place and then adding a float valve
or something similar in the pond. The easier way is simply to do the topping up yourself, using a hose pipe. Then you have to check the water level once a week and make sure the level is where it should be. If you have water lilies in your pond, you have to watch the level all the time, since they do not like the level to drop too low. In the case of the water feature under discussion, I concealed it between the shrubs and took it right back to the nearest tap, where I connect it from time to time and top up from there. In another system I tapped into my existing high pressure network and enjoy an automatic topping up by means of a small float valve.
Ball valve: 
Adding a waste tap (ball valve) is a good idea. Ideally one should insert one at the bottom of the pond leading out beneath the wall of the pond, but chances of leakages are rather big, so I suggest you don’t do that. However, the second best idea (with no chances of leakages) is by adding one at the back of the waterfall . You can insert a plastic “T”-connection anywhere where convenient (see picture above). If you do need to empty the pond this will help a lot.
Pond filters
All submersible pumps have built-in filters (which needs cleaning from time to time). However, an extra filter is recommended to curb floating algae and to help keeping the water cristal clear. You have a choice between mechanical filters, UV filters and biofilters. Mechanical filters are imperative when you have a big problem with leaves dropping into the pond. Biofilters and UV filters are necessary for dealing with algae and keeping the water clear. Some products are a combination of more than one type.