Cut Out Clogging Galvanized Waste Pipe and Lose Vent Stack Support?

The kitchen drain uses 2" galvanized piping that's fifty years old. It clogs up sometimes and I have to use the power auger drill attachment to get things moving again. There is the potential that the drain could decide to clog when the dishwasher is draining and nobody is around to prevent the flooding.
So, looking into replacing a section of galvanized pipe with PVC. It's all exposed in the basement so access is not a problem. What I noticed is that the pitch of the five feet of horizontal portion, before it reaches the 45 deg elbow going to the main waste line, is slightly in the wrong direction! So what I think is happening is the solids are settling back near the 90 deg sweap instead of heading downstream, thus choking of the sweep connecting the vertical portion coming from the sink to the horizontal section.
My fear is that the horizontal run is probably pitched wrong because it is supporting the weight of the galvanized vent stack that tees off of where the p-trap enters the line upstairs. Cutting out the horizontal portion of the galvanized pipe could then create more problems if everything shifted. I don't want to try too hard to jack up the horizontal pipe given its age, but if I could just a bit what could I use to suspend the galvanized from the floor joist above it? This stuff is pretty heavy.
Thanks!
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snipped-for-privacy@optonline.net wrote:

I was going to say: Buy or fabricate a clevis hanger: http://www.pipingtech.com/products/ptpcat/support/hanger/fig2.htm
1/4-20 all thread rod to joist with a plate bolted to joist.
But that only helps if you leave some of the horizontal run in place (at the EL). And it depends on the rotted galv threads in the EL to support the weight:-(
If there really is all the weight of 2" galv above the P-trap that you think there is, then the vertical pipe should get a support with a yoke bolted around it and strapped/bolted to joist(s).
THEN...you can saw off the vertical pipe to correct the slope problem. Replace the galv EL with a long-turn PVC sweep EL. Or...with a long-turn TEE-WYE and cleanout.
Jim
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snipped-for-privacy@optonline.net wrote:

There are supports that fit between studs/joists and hold the pipe.
Install one on the vertical pipe. Cut off as needed below that. Couple the old pipe to the new PVC with a Fernco rubber coupling.
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And make certain with a level that the horizontal pipe is actually sloping the wrong way before you start cutting.
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Metal pipe tape. Just loop it under the pipe and nail it to an exposed floor joist before cutting.
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