(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 6 of 6

Thread: Drilling holes in plastic tank

  1. #1

    Default Drilling holes in plastic tank

    Hi, I have a new 500 liter plastic potable tank to be installed in the attic and I need to drill a hole for an overflow pipe (which is 32 mm diameter).. What kind of drill bit is best and what diameter of hole is recommended? I also need to find a way to allow air into the tank while preventing dust and insects from entering. Any ideas? thank you.

  2. #2
    In the Trades Bob NH's Avatar
    Join Date
    Oct 2005
    Location
    New Hampshire
    Posts
    3,307

    Default

    I have used an expansion bit (The kind used with a "brace", as in "brace and bit", in the days when such things were done by hand).

    A hole saw will also work, or a spade bit.

    You can enlarge a hole by using a torch to heat up the edge and carving with a knife.

    You can make an effective and inexpensive bulkhead fitting from a PVC male adapter and a female adapter with a gasket cut out of a convenient piece of rubber. You can also seal with silicone. I have screwed the male part of the adapter into a softened area of a polethylene tank and used the female adapter as a nut to seal it.

    Most of the tanks that I have used have a vent in the cover. It is almost impossible to seal such a tank. Do you need a vent or an overflow?

    Keeping bugs out is difficult. I have put a piece of fine screen on the vent.

    You need to be sure that your attic is strong enough to support a 500 liter tank full of water. Most attics are not structurally designed to support such a large load and you could easily damage the ceiling (best case) or break the joists and have it collapse into the house (worse) or fall through and kill someone (worst case).
    Last edited by Bob NH; 07-14-2006 at 09:57 AM.

  3. #3

    Default

    yea, I know 500 lts is a lot. I wanted a smaller tank (350 lt) but not available just now at suppliers. My idea is to fill it to about 300 lts. Of course if one day the floating switch is faulty then the tank would fill right up to the overflow pipe...I suppose I could always put the overflow lower down in the tank to make 300 lts the max level... I will be resting the tank on short pieces of beams inserted into the wall and supported underneath with legs resting on the ceiling beams. BTW could I use a normal wood drill bit of about 28mm (1 inch) to cut the hole for the overflow?

  4. #4
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
    Join Date
    Nov 2005
    Location
    Central Florida
    Posts
    2,685

    Default

    If you know any avid RVers, borrow one of their magazines and look for ads from people who make custom tanks for potable, grey, and black water. They can cut holes, insert fittings, and generally do everything with plastic tanks for converted buses, new RVs, etc.

  5. #5
    In the Trades Bob NH's Avatar
    Join Date
    Oct 2005
    Location
    New Hampshire
    Posts
    3,307

    Default

    You can drill the hole with just about anything, and you can make it larger with a sharp pocket knife, especially if you soften it with a torch.

    I would be most concerned about wrecking your ceiling if it is not designed for the loads. Even if it doesn't collapse, it is likely to damage the finishes because of large deflections.

    Ceilings are rarely designed for more than 100 kg/square meter. A 500 liter tank full of water is about 500 kg/sq meter. If you reduce it to 300 liters then you will only be overloading it by a factor of three.

    You should not fill that tank until you or someone has made a number to show that it is safe. You need to analyze the structure from the attic all the way down to earth.

  6. #6

    Default

    About the weight of the tank - In my case two 1 meter beams will be inserted into a principal brick wall which is about 14 cms thick, taking about half the weight of the tank, and then two other short beams (80 cm) will act as legs, resting on two ceiling beams - or maybe I can spread the weight over three ceiling beams, by lying a short horizontal beam over the three beams. All the beams are 7,5cm x 12,5 cm thick and the ceiling beams are seperated by 60 cms. So I thought that since the tank will be next to a brick wall, the ceiling beams would be very strong at that point (the support legs resting about 80 cms from the wall) In any case I suppose I should limit the tank capacity to around 300 lts (with lower overflow pipe) to be on the safe side? Or do you think I should reduce it even more - 250 liters? which would be half the tank capacity.
    The present old uralite tank holds 200 lts and even when empty weighs maybe 50 kilos)
    Last edited by sprinkler; 07-15-2006 at 01:31 AM.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •