Holding tank sight tubes

Has anyone had luck installing sight tube on holding tank or do they just become unreadable? I was thinking (always dangerous) that if I installed with
petcock shut offs (to change out the clear tubing) from mid tank to top that this might work. Tired of finding out the tank is full the hard way. Tankwatch 3 sensors have given up. What do you think?

Sight glass is not the answer but if the tank is plastic and accessible try shining a high intensity light thru the side, you may be able to see the level. Tank level indicators fail because they get false readings off the residue that clings to the inside of the tank.

We have changed the sight tubes on two of our four saddle tanks. The other two have fuel in them so we are waiting until we draw the tanks down to empty with transfers to the day tank before I change the tubes.

I did a lot of research on what type of tubing to use and in the end I went with the recommendation to use flexible PVC tubing. There is another type of tubing that works very well, too, and is more resistant to dye absorbtion but to use it I would have had to buy an expensive 50' roll which was far more than I need or would ever use. So I went with the PVC. It will absorb fuel dye a little faster than the other type but it's inexpensive and I can buy just the amount I need.

FredB said:

Tankwatch 3 sensors have given up. What do you think?

Click to expand...

I've used and really like the Raritan non-contact level monitor - not inexpensive but it can handle multiple tanks if that's an advantage. Installation Manual

I installed it on 2 tanks (black & fresh water) and had zero issues in about 10 yrs

I would think that a sight tube of large enough diameter would work and be less susceptible to fouling.

Only experimentation would tell you how fast the sight tube may become cloudy enough before being useful.

A Harbor Freight digital temperature gun/sensor will detect the liquid level...seems to work best first thing in the morning as the air in the tank cools off more quickly than the liquid overnight.

Marin said:

There is another type of tubing that works very well, too, and is more resistant to dye absorbtion but to use it I would have had to buy an expensive 50' roll...

Click to expand...

I've always used rigid Tenite Butyrate Tubing, available in 6' lengths (I get mine at Laird Plastics in Seattle):


I'm not quite sure how I'd deal with flexible tubing - maybe sleeve it with...rigid tubing?

I wouldn't do this with a holding tank though - the last thing I want when looking at that is "optical clarity"!

There is a very good reason you almost never see sight tubes in black water tanks.

Replace your TankWatch sensor.

There are things in life you never wish to see again, the contents of the black water tank fall into that category.

No kidding! Sight tubes? Install a bright light as suggested or perhaps just weigh your guests before and after?

Sight tubes!

On big marine treatment systems I have installed only on the spill over tank after it has pasted thru the main aeration treatment tanks they use side mounted float level switch's "Big boys" as a back up they have sight glasses
The sight glasses had to be cleaned every week and the switch's every 2 months dirty but easy job
I would not use sight glasses on a raw waste tank they would plug and would be a bitch keeping clean .

On our personal boat we have 3 x 20 gallon holding tanks 5 heads
last year we installed air actuated ball valves on the tanks and replaced 2 of the heads from vacuum flush to Dometic grinder toilets.
Out of the three holding tanks the one collecting the waste from the living room kitchen dinning room main in the highest use so I need to put a sensor on it . It used to be a straight drop Sealand toilet into the tank now a grinder
So I'm on the search also for a sensor my primary tank

Since everything is ground up I'm expecting not to get build ups also I use a treatment that breaks up the waste to almost water. So the level should be the same across the tank .The tanks are fiberglass (but still viewable with a strong light)and thick so using outside proximity sensors will be a no go.
I will be ether going to a ultrasonic internal sensor or a simple floating ball on a cord "water float" both mounted top center of the tank as backup I will install a permanent light mounted on the outside clear section and flush so there is no bleed of light into the space.
Being cheap I will try the light first and the water float boating
Season is far away I have 4 months to get it done

...Harbor Freight temperature gun....doesn't need cleaning...~$30.

semi-planing said:

A Harbor Freight digital temperature gun/sensor will detect the liquid level...seems to work best first thing in the morning as the air in the tank cools off more quickly than the liquid overnight.

Click to expand...

I think you mean that after it all cools overnight, the air in the tank warms faster than the liquid?

Either way, I like the idea. I have one of those guns to keep an eye on trailer hubs/brakes/tires.

Here's what I installed on my non-metallic fresh water and holding tanks for about $100 each. They have worked flawlessly.

Monitoring Systems

we use one on our plastic holding tank, although with Purasan we seldom use it. Company has great customer service, our tank level indicator stripes didn't work, they shipped us replacements fast and that fixed the problem.

FF said:

Hart Systems - Home

Click to expand...

Tank Tender tubes are fairly small, and the one in my black water tank did block up. But careful pumping of the TT air knob over a period of time has cleared it. My blackwater tank is shallow in depth so its not particularly accurate anyway.

But I do like the TT system, and I think installing the 10 tank instrument was one of the best things the PO did. I have 6 fuel tanks and 2 water tanks on it as well as the black water tank. I mainly use the TT for the water tanks as the fuel tanks all have sight tubes and are easy to glance at when in the ER.

FlyWright said:

Here's what I installed on my non-metallic fresh water and holding tanks for about $100 each. They have worked flawlessly.

Monitoring Systems

Click to expand...

X2.