In case you were wondering, the amounts reported as the built in gain are based on the fair value of ET units received on the merger date (10/18/2018) -- approx $17.05/unit -- less your closing ETP partner  capital account balance "withdrawal" (subtract any Box 19 distributions included in this amount) per Part II, section L on your K-1.  This ETP withdrawal amount/ending ETP capital account is your adjusted basis in your new ET units.  Continue reporting all ETP K-1 items using the separate schedule provided by ETP and ET in 2018, and ET in future years.  All ETP Suspended losses will be recognized when you sell your ET units. ... View more

here is the full text of IRS instruction:  Item M If you have contributed property with a built-in gain or loss during the tax year, the partnership will check the “Yes” box. Also, the partnership will attach a statement showing the property contributed, the date of the contribution, and the amount of any built-in gain or loss. A built-in gain or loss is the difference between the fair market value of the property and your adjusted basis in the property at the time it was contributed to the partnership. If you contributed more than 10 properties on a single date during the tax year, the statement may instead show the number of properties contributed on that date, the total amount of built-in gain, and the total amount of built-in loss. The partnership is providing this for your information. Contributions of property with a built-in gain or loss could affect a partner's tax liability (in matters concerning precontribution gain or loss, and distributions subject to section 737), and may also affect how the partnership allocated certain items on your Schedule K-1. For information on precontribution gain or loss, see the instructions for box 20, code W. For information on distributions subject to section 737, see the instructions for box 19, code B. ... View more

I don't believe so, assuming you still owned ET at 12/31/2018 ... see IRS Partner's Instructions for Schedule K-1 (Form 1065), Part I, item M (checked yes on my ET K-1).  Since no box 20, code W, and no "distributions subject to section 737, see the instructions for box 19, code B", on my ET K-1, it appears this statement is FYI only, for use at some future date when you dispose of your ET units. ... View more