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385 holding tank upgrade?

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Category: Hints and Tips
Forum Name: 385
Forum Description: 385 Hints, Tips and News
Printed Date: 23 October 2019 at 17:31
Software Version: Web Wiz Forums 12.01 -

Topic: 385 holding tank upgrade?
Posted By: P&H
Subject: 385 holding tank upgrade?
Date Posted: 04 August 2018 at 05:47
Hi all

Anyone have any experience or ideas on how to increase the holding tank capacity? We love our 385 but holding tank size a challenge without “rationing” and we are planning some longer cruises next year. 

BTW fitted the Gobius tank sensor which works really well. 


Posted By: Fendant
Date Posted: 04 August 2018 at 07:53
Hello Phil,

I fitted on my 345 an additional 50 litr stainless steel holding tank behind the wall in the shower compartment. This one is connected to the ridiculous small Hanse reservoir of 25 - 30 ltr capacity. On the added tank I am using a Philippi ultrasonic sensor.


Posted By: alidal
Date Posted: 04 August 2018 at 08:29
This is what`s done on a 400.." rel="nofollow -

Hanse 400#655

Posted By: P&H
Date Posted: 05 August 2018 at 16:07
thanks - that is the kind of approach I was thinking of if only I can find a space big enough. 

Did you connect the new tank upstream of the old tank and higher than the original so you still have a single seacock to release the contents with the aid of gravity? Also do you still have a single deck cap for a pump out?


Posted By: P&H
Date Posted: 05 August 2018 at 16:18
thanks - looks a great solution 

Posted By: Fendant
Date Posted: 05 August 2018 at 17:13
Hi Phil,
I am not allowed to discharge anything into the water. So I only have the deck pump out fittings.
The new tank is downstream from the factory installed plastic tank, it has its separate vent and pump out fitting.
Both vents are above the max leve of the plastic tank. Connection between the two is via a special sanitary hose.
The lower tank has the ultrasonic sensor, on the plastic tank I am continuing to use the Gobius sensor system.
The max level in the lower tank is about the 50% level of the plastic tank.
For pump out it is sufficient to open only the deck fitting of the plastic tank.
I can only strongly suggest to build a wooden / cardboard model first. With this you can try out the fitting into the confined space and most importantly check the access for the pipe connectors, the level sensor and how to fit the pipe onto the connectors incl. double jubilee clips.  It would also make sense to install a filter into the vent hose, which needs to be changed annually or biannually ( of your course not needed if you are always in cold waters ). If you are satisfied, then you can make a rough sketch and approach some stainless steel shops. Include threaded flanges for the sensor and the pipe fittings.


Posted By: P&H
Date Posted: 11 August 2018 at 08:51
Thanks Frank - very useful info.

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