Short answer. On expiration of the redemption period the purchaser is substituted to and acquires all the rights, title, interest and claim that the judgment obligor had in the property as of the time of the levy. Nothing more than that, and measured from the levy date.
What the law says
Upon the expiration of the right of redemption, the purchaser or redemptioner shall be substituted to and acquire all the rights, title, interest and claim of the judgment obligor to the property as of the time of the levy.
Rule 39, Section 33 — Deed and possession to be given at expiration of redemption period; by whom executed or given. Read the full provision →
You step into the debtor's position, not into a clean title
The rule transfers what the judgment obligor had and nothing beyond it. If the debtor owned the property outright, that is what passes. If the debtor held it subject to an existing encumbrance, held only an undivided share as a co-owner, or held under a defective title, the purchaser takes it in that same condition. This is the most important thing to understand before bidding at an execution sale. The auction determines who succeeds to the debtor's position; it does not improve that position or cure the problems attached to it.
The date that matters is the levy, not the sale
The rights acquired are those the judgment obligor had as of the time of the levy. That earlier date is deliberate. It means dealings the debtor entered into after the levy cannot cut down what the purchaser eventually receives, and equally that rights already in existence at the time of the levy are not swept away by the sale. Anyone assessing what is actually being bought should therefore be looking at the state of the property as of the levy date, which may be many months before the auction was held.
When the substitution takes effect
The substitution happens upon the expiration of the right of redemption, not at the fall of the hammer. Until then the judgment obligor has the entire period of one year from the date of the registration of the sale in which to redeem the property. A purchaser during that year holds something short of ownership. The deed is executed by the officer making the sale or by his successor in office, and the rule provides that a deed executed by a successor has the same validity as though the officer making the sale had continued in office and executed it.
The limit on taking possession
Acquiring the debtor's rights is not the same as being able to walk in. The rule directs the officer to give possession to the purchaser or last redemptioner unless a third party is actually holding the property adversely to the judgment obligor. Where such an occupant exists, possession is not delivered through the execution process at all, and the buyer is left to an ordinary action against that person. Anyone valuing a property at auction should look closely at who is on it, because that single fact can delay possession considerably.