[montr]

Originally Posted by rulonger

Could you post a picture of your invention?

The picture in post #78, show the siphon and the brass adapter to a smaller tubing. There is nothing special there, the parts are available at HD or Lowes for few $.

To prevent any leak, I used silicon tape to seal all the connections.

[die$el<3]

Thanks for this, it was really helpful just filled both my tanks and it went much quicker then I anticipated.

[taibanl]

No inventions needed. The mb filler hose and the mb 10L jug (refillable) make this painless and effortless

[POBEP]

Originally Posted by Persian Whisperjet

I would recommend doing what montr said. Just buy 2.5 gals, and put it all in the passive tank. That will get you a solid 7,500 miles, and the DEF you put in six months from now will be that much fresher. Also, if you put it all in the passive tank the pumping circuitry will have to work more to move it to the active tank, which is good since the enemy is crystallization and clogging.

Apology for reviving old DEF thread.

Context: I have 3 diesels E70, F25 and most recent addition E90.

Based on my community and BMW SCR & SCR 2 readings, keeping system "wet and not overfilled" should help function it correctly.
You probably should avoid
- overfilling any of your tanks (this is no news)
- allow passive tank run dry (e.g. keep transfer line "wet").

It makes it a bit tricky, but simple spreadsheet math based on DEF consumption rate could be good reference when to refill (passive) tank.

TL; DR

F25
It has single filling port.
It "magically" refills active fist, then remaining goes in passive.
Active/Passive tank placement combined with gravity makes refill no different from filling washer fluid.
No transfer pumping involved at the fill time.

E70
SCR DEF lines, pump, tanks are original, odometer at 99,578mi
NOx sensors and SCR Cat was replaced at ~79,950mi
Just like E90, 2 ports, passive under air filter intake duct.
I never fill active - passive only.
I fill 0.5gal Kruse bottle from 2.5G Peak jug, tilt intake duct, repeat 5 times.
The transfer pump kicks in when second bottle is being filled.
By the time I am done with fill up the warning message is gone.

E90
First DEF refill since taking over ownership.
DEF tanks were replaced according to previous owner.
Counter was at 961 miles.
The battery is not great, connected to 10A charger.
Turned ignition on.
Just like with on E70, on a second Kruse bottle transfer pump kicked in.
2.5G went into passive without an issue.
Warning message went away.

I left ignition ON to let the transfer pump finish its job.
The transfer pump stopped after 1 hour.
1000mi no start message came up (yes, 1000, not 999)

ISTA+ DEF refill detection service function helped message to go away.

Here are my thoughts/observations.
1) When DDE detects DEF refill conditions, it will try to pump enough DEF into active until
- active tank is at the FULL level (from BMW SCR doc), OR
- passive tank reached EMPTY level (from BMW SCR doc)
- 60 min of transfer pumping (personal experience above)
2) BMW SCR doc says that if active tank is depleted below certain (unspecified) level, the transfer pumping will NOT get activated at all until Active tank is refilled to the "FULL" level.
Hence, they recommend filling Active first (which most of us do not do for well discussed reasons)
3) The BMW DEF refill logic detection is not perfect along with buggy tank level sensors.
Hence, some of us may experience a scenario where counter does not reset immediately after refilling (passive) tank.
4) Clogged transfer line could make transfer pump job challenging.
This is where 1 hour transfer failed for me (active tank got to 80% level, above warning threshold, with sufficient media available in the passive tank)

Just like with E70, I am going to keep my Passive tank level above empty but below full at all times
HTH