gutering as mentioned or whatever size plastic pipe you require,spread aqurium sealent all over it get the same gravell thats in your tank.make sure its clean and dry,spread the gravell evenly on paper then roll the pipe or guttering over the gravell while sealent is still wet,and it will completely cover it and also helps it to stay on the bottom of your tank due to the extra weight of the gravell,also leave it to dry fo 24hrs bfore placing in tank
mister-t