Newbie making first wet dry DIY
 

Making my first wet dry filter for my 100gallon. can i restrict the flow of a 1000gph with a ball valve?

you should be able to,just get the correct size.

alright. thanks alot. any advice on making a 1.5" siphon?

1st when choking back a pump be sure to have a T off that goes back to the other side of the wet/dry this is where the ball valve will go and you regulate flow there if you dont use this the pump will burn out rather fast (about 1/2 its normal life if not faster)
2nd are you looking to make a PVC overflow or a box type? if you Google it or search youtube you will find a lot of great step by step vids... but be careful as some of those need modifications that they did not show... for example the PVC overflows need a check valve installed at the top of the bend over the wall i neglected this step in mine (before changing designs) and it kept failing

is a check valve just an air line at the top? Is a 1.5" siphon sufficent for a 100 gallon or do i need bigger?

a check valve is sold as a part for an airline .. it alows flow in one direction if set up properly this will alow trapped air to escape and the siphon will not break.. 1.5 inches is more than enough

so i just need to drill a hole on the top of the siphon and place the check valve in it?

it needs to be sealed in but yes .. again search youtube and look at designs that incorporate this and you will see how its done....

I got the check valve. should i place it directly to the pvc or should i run an air line then connect it?

what i have seen (again i do not use this so any one with experience please jump in here) drill a hole to fit the valve and ten super glue it in adding some silicone for added barrier... be sure that it is set to flow away from the PVC to let air out... not let air in or you will be sure to have issues